June 25, 2012 -- Older women with low blood levels of vitamin D may be more prone to pack on the pounds, when compared with women who have adequate vitamin D levels.

Of more than 4,600 women aged 65 and older, those with insufficient levels of vitamin D in their blood gained about two pounds more than those who had adequate levels of the vitamin during a five-year study.

The women with insufficient levels of vitamin D also weighed more when the study began than women with normal vitamin D levels.

"Lower vitamin D levels are associated with more weight gain in older women, but the weight gain was relatively small," says researcher Erin LeBlanc, MD. She is an endocrinologist and researcher at the Kaiser Permanente Center for Health Research in Portland, Ore.

The findings appear in the Journal of Women's Health.

Most women in the study had less than 30 nanograms per millimeter (ng/ml) of vitamin D in their blood. Insufficient vitamin D levels are defined by The Endocrine Society panel as being below 30; vitamin D deficiency is defined as levels below 25.

The women with insufficient levels of vitamin D also weighed more when the study began than women whose vitamin D levels were 30 ng/ml or above.

In the group of 571 women who gained weight, those who had insufficient vitamin D levels gained about two pounds more than women who had sufficient vitamin D levels, the study shows.

The study can't say whether low vitamin D is causing the weight gain or just reflecting it. "The study is the first step that we need to evaluate whether vitamin D might be contributing to weight gain," LeBlanc says.

But there are some theoretical ways that low vitamin D could contribute to weight gain, she says. Fat cells do have vitamin D receptors. "Vitamin D could affect where fat cells shrink or get bigger."

"There is a lot that goes into vitamin D levels: sun exposure, age, diet, pigmentation," LeBlanc says. "Talk to your primary care providers about screening and whether or not you need to take supplements."

Getting Enough Vitamin D

Vitamin D is called the sunlight vitamin because our bodies produce vitamin D when exposed to the sun. Vitamin D is also added to milk and other foods, and is available in small amounts in fatty fish like tuna, salmon, and mackerel; beef liver, cheese, and egg yolks. But it can be hard to get as much as we need from our diets. As a result, supplements are often needed.

The Institute of Medicine recently raised the recommended daily intake to 600 IU for people aged 1-70 and to 800 IU for adults older than 70. Other groups set the bar even higher.

Robert Graham, MD, says that the new study adds another piece to the vitamin D puzzle. He is an internist at Lenox Hill Hospital in New York City. "We can't say that vitamin D is the cause of weight gain or an effect of it," he says. "We can say that everyone should have sufficient blood levels of vitamin D."

His advice? Go get your levels tested -- and supplement if necessary to make sure your levels are 30 nanograms per millimeter or above. "Eating a healthy diet and engaging in regular physical activity is also key to maintain a healthy weight."

SOURCES: Erin LeBlanc, MD, endocrinologist and researcher at the Kaiser Permanente Center for Health Research in Portland, Ore.Robert Graham, MD, internist at Lenox Hill Hospital in New York City.LeBlanc, E.S. Journal of Women's Health, 2012, study received ahead of print.